Demetrius of Phaleron was an Athenian orator, statesman, and philosopher who lived from approximately 350 to 280 BCE. A student of Theophrastus, he belonged to the Peripatetic school of philosophy. After Athens's defeat by Macedon, he was installed as governor of Athens from 317 to 307 BCE with Macedonian backing. His rule was a moderate oligarchy that provided stability at the cost of democratic freedoms. He was driven into exile following the city's capture by a rival Macedonian leader.

Demetrius then went to Alexandria in Egypt, where he served as an advisor to King Ptolemy I. Ancient sources credit him with a significant role in proposing the creation of the Library and Museum of Alexandria, though the exact nature of his contribution is debated by modern scholars. He later fell from favor and died in Egypt around 280 BCE.

He was a prolific writer, but none of his works survive intact. They are known only through fragments and later references. His writings covered history, philosophy, and rhetoric, with notable lost works including On Fortune and On the Athenian Legislation. He is also credited with compiling the first written collection of Aesop's fables. A surviving rhetorical treatise, On Style, was traditionally attributed to him, but scholars now believe it was written by an unknown author centuries later.

Demetrius is historically significant as a bridge between the Classical Greek world and the Hellenistic kingdoms. His career exemplifies the philosopher-statesman ideal, and his move to Alexandria symbolizes the transfer of Greek intellectual culture. His legendary connection to the Library of Alexandria has made him a notable figure in the story of ancient scholarship.